I. Formation of the Earth • Around 4.7 billion years ago, a young nebula in the middle of a Milky Way spiral arm existed • Nebulae are full of gas and dust, the birthplace of stars • A large clump of gas and dust coalesced in the nebula and accreted more mass over time • It began spinning, and pulled some matter around it in a disk
Formation of the Earth • The matter in the disk began accreting into clumps • Very large clumps attracted a lot of matter to them and gained mass • They became planets • Less successful (smaller objects) included comets and asteroids • Eventually, as most of the mass went to the sun, it spun up even faster and the objects in the disk sped up and rotated too quickly for mass to accrete. Then, collisions and ejection occurred.
Formation of the Earth • The Earth became one of the inner (terrestrial) planets that escaped ejection • It formed around 4.6 billion years ago • We estimate its age from meteorites, which are largely unchanged from formation, as plate tectonics on the Earth destroy most older rocks • The Early earth was molten, with hydrogen and helium in its atmosphere • Moon formed by a Mars-sized object (“Theia”) hitting earth 4.5 billion years ago and flinging a lot of the mantle into space
Formation of the Earth • The Earth had cooled since its formation and was able to develop oceans beginning during the heavy bombardment (3.8 – 4.1 billion years ago) • Lighter gases (hydrogen and helium) had already escaped Earth’s gravity and were lost to space • Water vapor in the atmosphere from volcanic outgassing and water vapor coming from asteroid and comet impacts condensed in the atmosphere • It precipitated very heavily and eventually the Earth had oceans
II. Earth is Unique • Basically, Earth has kept water in three phases (not too hot like Venus or too small to keep it like Mars) for most of the past 4 billion years, particularly most of the past 1.5 billion years • The sun is a single, very stable star, with a long life • The moon has helped stabilize Earth’s axial tilt, which greatly reduces climate fluctuations • Jupiter is at just the right distance to deflect the vast majority of comets and asteroids from earth-approaching orbits, and no gas giants have made it more dangerous since the period of heavy bombardment, and Jupiter is far enough that it doesn’t disrupt Earth’s orbit
Earth is Unique • Water can dissolve organic (carbon-based) compounds, necessary for life • Water has one of the highest specific heats of any known substance and also high value of latent heat, and this stabilizes climate • Liquid water expands as it cools (rare occurrence), which greatly reduces the speed of freezing • Carbonic molecules can dissolve or stay intact in a water solution; carbon can create covalent bonds with many nonmetals, and, with water, can form carbohydrates, import for other biochemical reactions • No one has been able to think of a substance which can support life nearly as well as water
Earth is Unique • We are situated in a relatively calm part of the galaxy, with minimal violence subjecting Earth from outside sources • No nearby supernovae or close solar-system directed ray bursts have roasted our planet for at least 4 billion years • As such, the Earth has had an incredibly ideal period for producing carbon-based life the past 4 billion years • Massive enough planet to retain atmosphere and for iron and heavy metals needed for skeletal structure and support/protection of head and large brains • Earth was able to store carbon dioxide in rocks, while sufficient plants allow for adequate oxygen and ozone production needed for cellular respiration • We do not know exactly how rare Earth’s situation is in the universe.
Earth is Unique • In addition, assuming that life would try to occur in any halfway conducive environment (big assumption), evolution does not necessarily have a “goal” regarding what type of life it creates • Survival of the fittest does not mean that intelligent beings capable of manual dexterity (ability to use hands) to form technology is a goal; there are a lot of intelligent vertebrates, and remember vertebrate life is EXTREMELY fragile • So, if life does exist on other planets (probably quite likely), they are not necessarily beings able to ponder and think in an objective, rational, moral, transcendent manner and also utilize tools for advanced technology
III. The Drake Equation • The past few decades, attempts have been made to quantify the likelihood of life with technology, such as ourselves, capable of contacting other planets, or being detected • N = R x Fp x Ne x Fl x Fi x Fc x L • N = number of civilizations in Milky Way that are capable of communicating • R = average rate of star formation in the Milky Way • Fp = fraction of stars with planets • Ne = average number of planets with potential to support life per star having planets (Fp) • Fl = Fraction of Ne that develop life • Fi = Fraction of Fl that develop intelligent life • Fc = Fraction of Fl that can release signals of their life into space • L = length of time Fc actually release such signals wikipedia.org
The Drake equation • N = R x Fp x Ne x Fl x Fi x Fc x L • R ~ 10 stars per year formed in our galaxy • Fp ~ 0.5 ? (half of stars will have planets) • Ne ~ ?? (0.1?) planets capable for life • Fl ~ 0.5? Capable planets that develop life • Fi ~ ???? Life becomes intelligent (very small) • Fc ~ ???? Life able to communicate (very small) • L ~ 10,000 years (communication last for 10,000 years) • Fc and especially Fi are probably tiny, just that we don’t know how small (.001 each, or 1 x 10-12 each??) wikipedia.org
What to take away Beings with technological capabilities similar to humans are a very rare occurrence in the galaxy (and universe) …It’s not what you see in science fiction!! Most planets certainly do not have them In fact, it may be possible that we are the only such type of beings which exist on any planet in the universe
IV. Meteor Showers • Meteors are typically the size of sand grains • They originate from comets and asteroids, whose orbits happen to cross near Earth’s orbit and have debris which burns into atmosphere • The small particles burn up in the ionosphere and leave a brightly ionized trail that we see • More particles earlier on in the solar system, when it was a lot messier
Meteor Showers • Favor Northern Hemisphere currently by chance • Most activity from mid-October through the first week of January • Interference of clouds or moon can be ruinous • Particularly intense displays (> 1000/hour) are called meteor storms– rare & incredible
Meteor Showers • Meteors visible every clear night • Sporadic meteors from random sources and meteors from distinct sources • Consistent high rates of meteors from distinct sources create the most popular meteor showers • Meteor showers have meteoroids with different ages, orbital periods, brightness distributions, rates, angles of hitting earth, speeds, mass distributions, total durations
Meteor Showers Combination of IMO rates, P. Jenniskens, E. Lyytinen, and my opinion
Meteor Shower • To see a meteor shower well, get well away from a city and its suburbs • Do not want any clouds or moon in sky (crescent moon is alright) • Typically peak in darkness just before morning twilight begins, when we are face-first in our orbit • Radiant must be high in order to see most of meteors
Meteor Showers • Best four overall for seeing lots of numbers in St Louis area and Northern Hemisphere midlatitudes are the Geminids, Perseids, Quadrantids, and Orionids • Geminid radiant is ideally placed in the sky and the best bet of seeing a high rate • Radiant is nearly overhead (maximum number of meteors visible) and is highest well before dawn • Also, a bright shower with fairly long maximum
V. Meteor Storms • Some meteor showers can have intense outbursts called meteor storms • Most storms last typically 1/2 hour or so. Occasionally longer-lived (Leonids and Draconids at times). The center of a high density comet trail istypically quite thin, so Earth plows through it quickly. • The Leonids, Draconids, Alpha Monocerotids, and Lyrids are all definitely capable. The June Bootids, Tau Herculids, Ursids,and Aurigids may be. It is uncertain whether the Sigma Ursids (next table) will evan materialize in 2014 (and also possibly 2019). • The Leonids and Draconids are the best known and most consistent (frequent, regular) meteor showers that produce meteor storms- at least for the past 100 to 200 years.
Possible upcoming meteor storms for U.S. and Europe. Predictions based on P. Jenniskens, E. Lyytinen, J. Vaubaillon, M. Maslov, and S. Molau
Possible Future Meteor Storms • Best Bets: 2034 Leonids (moonless) and 2037 Leonids • Other decent chances: 2045 June Bootids (moonless), 2022 Tau Herculids (moonless- this one could be nothing or completely spectacular or somewhere in between), 2035 Leonids, 2028 Perseids, and 2043 Alpha Monocerotids • All in table worth a shot if you’re in the area • Other storms possible, with some lesser likelihood predictions (not shown) and unknown sources the cause, the latter of which are unfortunately not predictable at this time